The starting towers in connection with ski jumping hills are usually constructed of concrete or timber. Such starting towers involve very high costs, and often furthermore they have an effect spoiling the scenery. Because they rise remarkably over the rest of the terrain, the wind quite often interferes with the starting run. This, as well as differences in the sliding of different skiers' skis may give the jumpers considerably different ultimate velocities. Especially owing to the high cost, good ski jumping hills are comparatively sparse and quite often the ski jumpers cannot train at the locality where they live.